Emergent carrier selectivity at dynamic semiconductor–catalyst–electrolyte junctions

Conventional models treat carrier-selective contacts on semiconductors as static Schottky or heterojunction barriers set by equilibrium energetics. In photoelectrochemical systems, however, the contact is a chemically active catalyst in an electrolyte, and its interfacial state evolves under illumination and bias. We show that electron and hole selectivity can emerge dynamically from coupled interfacial redox chemistry that reshapes the effective barrier heights at the semiconductor–catalyst junction. Using operando ambient-pressure X-ray photoelectron spectroscopy as a wireless, element-specific potential probe, together with dual-working-electrode and photoelectrochemical measurements, we track how initially weakly selective interfaces on oxide photoelectrodes become strongly hole- and electron-selective catalytic contacts during operation. The mechanisms are relevant to particle-based overall water splitting and, more broadly, to dynamic electrochemical interfaces.